1. Field of the Invention
The present invention relates generally to stents and other prostheses intended for implantation in blood vessels and other body lumens. In particular, the present invention relates to methods and articles for the fabrication of such stents.
The use of stents and other luminal prostheses is often indicated when there is desire to maintain patency of a body lumen. Stents have commonly been used in blood vessels, the ureter, and the biliary duct, for the treatment of conditions which can result in luminal obstruction. Of particular interest to the present invention, vascular stents have demonstrated significant success in inhibiting restenosis following angioplasty and other primary interventional treatments in the vasculature. Lined stents, often referred to as vascular stent grafts or prostheses, hold great promise for the reinforcement of blood vessels for the treatment of aneurysms and lining of blood vessels for the treatment of occlusive disease among other conditions. In the case of aneurysms, the stent acts as a scaffold or framework for supporting the liner within the blood vessel to define an artificial lumen therethrough. In the case of occlusive disease, the stent maintains lumenal patency while the liner inhibits cellular intrusion into the lumen.
Vascular stents are typically delivered in a radially reduced or constrained configuration and expanded in situ at the target site. The stents may be deformable and balloon-expanded at the target site. Alternatively, the stents may be formed from a resilient material and released from constraint to self-expand at the target site. In a third general approach, the stents are formed from a shape-memory alloy and induced to expand at the target site by exposure to a temperature change. In all such cases, the stent will usually comprise a network or lattice of structural elements which permits configuration in both the radially-reduced and the radially-expanded geometries. One common geometry comprises a plurality of lozenge-shaped or diamond-shaped elements which are joined in a ring and may be expanded from a small diameter configuration to a large diameter configuration. Other common geometries include helically wound wires and filaments, zig-zag rings, serpentine rings, and numerous combinations and derivations of these geometries.
Regardless of the particular stent geometry chosen, manufacture of the stent presents a number of technical challenges. The stents have very small dimensions, often with diameters of 1 mm and below, and may be formed from metals and alloys that are difficult to fabricate, such as shape memory alloys and stainless steel alloys having specific properties. It will be appreciated that the stents which are produced must have highly uniform expansion characteristics, and thus the fabrications methods should result in stents having highly uniform mechanical properties. Moreover, the dimensions must meet very close tolerances and the surface finishes of the stents must be non-injurious and non-thrombogenic.
The most common methods for producing vascular and other stents start with a tube which is then cut or otherwise patterned to have the desired geometry. In many cases, particularly with shape memory alloys, it will be further necessary to heat-treat the resulting stent in order to gain desired expansion properties. Cutting of the tube stock starting material can be effected in a variety of ways. Most commonly, laser cutting is employed. Laser cutting, however, results in significant thermal stresses on the material which can be particularly troublesome when producing shape memory alloy stents. Chemical etching of the tube starting materials have also been proposed. Patterning and etching of tubes, however, is very difficult and expensive to perform.
For these reasons, it would be desirable to provide improved methods and articles for manufacturing cylindrical stents. Such improved methods should preferably be compatible with a wide variety of starting materials, including shape memory alloys, stainless steel alloys, and other materials from which stents are commonly performed. Such methods and articles, moreover, should preferably expose the materials to minimum thermal and other stresses, thus enhancing the dimensional and physical stability of the resulting stents. The present invention will address at least some of these objectives.
2. Description of the Background Art
Methods for laser cutting tube stock are described in U.S. Pat. No. 5,073,694. Methods for etching tube stock to produce vascular stents are described in U.S. Pat. No. 5,421,955. Methods for fabricating stents by winding a serpentine element over a cylindrical mandrel are described in U.S. Pat. No. 5,019,090.